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Smith, Tanya

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Smith

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Tanya

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Smith, Tanya
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Now showing 1 - 10 of 26
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    First Molar Eruption, Weaning, and Life History in Living Wild Chimpanzees
    (Proceedings of the National Academy of Sciences, 2013) Smith, Tanya; Machanda, Zarin; Bernard, Andrew B.; Donovan, Ronan M.; Papakyrikos, Amanda M.; Muller, Martin N.; Wrangham, Richard
    Understanding dental development in chimpanzees, our closest living relatives, is of fundamental importance for reconstructing the evolution of human development. Most early hominin species are believed to show rapid ape-like patterns of development, implying that a prolonged modern human childhood evolved quite recently. However, chimpanzee developmental standards are uncertain because they have never been based on living wild individuals. Furthermore, although it is well established that first molar tooth emergence (movement into the mouth) is correlated with the scheduling of growth and reproduction across primates broadly, its precise relation to solid food consumption, nursing behavior, or maternal life history is unknown. To address these concerns we conducted a photographic study of subadult chimpanzees (Pan troglodytes schweinfurthii) in Kanyawara, Kibale National Park, Uganda. Five healthy infants emerged their lower first molars (M1s) by or before 3.3 y of age, nearly identical to captive chimpanzee mean ages (∼3.2 y, n = 53). First molar emergence in these chimpanzees does not directly or consistently predict the introduction of solid foods, resumption of maternal estrous cycling, cessation of nursing, or maternal interbirth intervals. Kanyawara chimpanzees showed adult patterns of solid food consumption by the time M1 reached functional occlusion, spent a greater amount of time on the nipple while M1 was erupting than in the preceding year, and continued to suckle during the following year. Estimates of M1 emergence age in australopiths are remarkably similar to the Kanyawara chimpanzees, and recent reconstructions of their life histories should be reconsidered in light of these findings.
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    Teeth and Human Life-History Evolution
    (Annual Reviews, 2013) Smith, Tanya
    Modern humans differ from wild great apes in gestation length, weaning age, interbirth interval, sexual maturity, and longevity, but evolutionary anthropologists do not know when these distinctive life-history conditions evolved. Dental tissues contain faithful records of birth and incremental growth, and scholars suggest that molar eruption age, tooth wear, growth disturbances, tooth chemistry, and/or tooth calcification may provide insight into the evolution of human life history. However, recent comparative approaches and empirical evidence demonstrate that caution is warranted when inferring hominin weaning ages or interbirth intervals from first molar eruption, tooth wear, or growth disturbances. Fine-scaled studies of tooth chemistry provide direct evidence of weaning. Early hominin tooth calcification is more ape-like than human-like, and fully modern patterns appear only after Neanderthals and Homo sapiens diverged, concurrent with changes in cranial and postcranial development. Additional studies are needed to relate these novel calcification patterns to specific changes in life-history variables.
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    Barium distributions in teeth reveal early life dietary transitions in primates
    (2013) Austin, Christine; Smith, Tanya; Bradman, Asa; Hinde, Katie; Joannes-Boyau, Renaud; Bishop, David; Hare, Dominic J.; Doble, Philip; Eskenazi, Brenda; Arora, Manish
    Early life dietary transitions reflect fundamental aspects of primate evolution and are important determinants of health in contemporary human populations1,2. Weaning is critical to developmental and reproductive rates; early weaning can have detrimental health effects but enables shorter inter-birth intervals, which influences population growth3. Uncovering early life dietary history in fossils is hampered by the absence of prospectively-validated biomarkers that are not modified during fossilisation4. Here we show that major dietary shifts in early life manifest as compositional variations in dental tissues. Teeth from human children and captive macaques, with prospectively-recorded diet histories, demonstrate that barium (Ba) distributions accurately reflect dietary transitions from the introduction of mother’s milk and through the weaning process. We also document transitions in a Middle Palaeolithic juvenile Neanderthal, which shows a pattern of exclusive breastfeeding for seven months, followed by seven months of supplementation. After this point, Ba levels in enamel returned to baseline prenatal levels, suggesting an abrupt cessation of breastfeeding at 1.2 years of age. Integration of Ba spatial distributions and histological mapping of tooth formation enables novel studies of the evolution of human life history, dietary ontogeny in wild primates, and human health investigations through accurate reconstructions of breastfeeding history.
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    Tracking cellular-level enamel growth and structure in 4D with synchrotron imaging
    (Elsevier, 2012) Tafforeau, Paul; Zermeno, John P.; Smith, Tanya
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    Variation in Enamel Thickness Within the Genus Homo
    (Elsevier BV, 2012) Smith, Tanya; Olejniczak, Anthony J.; Zermeno, John P.; Tafforeau, Paul; Skinner, Matthew M.; Hoffmann, Almut; Radovčić, Jakov; Toussaint, Michel; Kruszynski, Robert; Menter, Colin; Moggi-Cecchi, Jacopo; Glasmacher, Ulrich A.; Kullmer, Ottmar; Schrenk, Friedemann; Stringer, Chris; Hublin, Jean-Jacques
    Recent humans and their fossil relatives are classified as having thick molar enamel, one of very few dental traits that distinguish hominins from living African apes. However, little is known about enamel thickness in the earliest members of the genus Homo, and recent studies of later Homo report considerable intra- and inter-specific variation. In order to assess taxonomic, geographic, and temporal trends in enamel thickness, we applied micro-computed tomographic imaging to 150 fossil Homo teeth spanning two million years. Early Homo postcanine teeth from Africa and Asia show highly variable average and relative enamel thickness (AET and RET) values. Three molars from South Africa exceed Homo AET and RET ranges, resembling the hyper thick Paranthropus condition. Most later Homo groups (archaic European and north African Homo, and fossil and recent Homo sapiens) possess absolutely and relatively thick enamel across the entire dentition. In contrast, Neanderthals show relatively thin enamel in their incisors, canines, premolars, and molars, although incisor AET values are similar to H. sapiens. Comparisons of recent and fossil H. sapiens reveal that dental size reduction has led to a disproportionate decrease in coronal dentine compared with enamel (although both are reduced), leading to relatively thicker enamel in recent humans. General characterizations of hominins as having ‘thick enamel’ thus oversimplify a surprisingly variable craniodental trait with limited taxonomic utility within a genus. Moreover, estimates of dental attrition rates employed in paleodemographic reconstruction may be biased when this variation is not considered. Additional research is necessary to reconstruct hominin dietary ecology since thick enamel is not a prerequisite for hard-object feeding, and it is present in most later Homo species despite advances in technology and food processing.
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    Developmental variation of the primate dentition: The 2011 AAPA symposium in honor of Don Reid
    (Wiley-Blackwell, 2011) Smith, Tanya; Guatelli-Steinberg, Debbie
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    Properties of tooth enamel in great apes
    (Elsevier BV, 2010) Lee, James J.-W.; Morris, Dylan; Constantino, Paul J.; Lucas, Peter W.; Smith, Tanya; Lawn, Brian R.
    A comparative study has been made of human and great ape molar tooth enamel. Nanoindentation techniques are used to map profiles of elastic modulus and hardness across sections from the enamel–dentin junction to the outer tooth surface. The measured data profiles overlap between species, suggesting a degree of commonality in material properties. Using established deformation and fracture relations, critical loads to produce function-threatening damage in the enamel of each species are calculated for characteristic tooth sizes and enamel thicknesses. The results suggest that differences in load-bearing capacity of molar teeth in primates are less a function of underlying material properties than of morphology.
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    Dental tissue proportions in fossil orangutans from mainland Asia and Indonesia
    (Asian-Australian Association of Paleoanthopologists, 2011) Smith, Tanya; Bacon, Anne-Marie; Demeter, Fabrice; Kullmer, Ottmar; Nguyen, Kim Thuy; de Vos, John; Wei, Wang; Zermeno, John P.; Zhao, Lingxia
    Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past million years. While studies have documented variation in dental tissue proportions among species of Homo, little is known about variation in enamel thickness within fossil orangutans. Here we assess dental tissue proportions, including conventional enamel thickness indices, in a large sample of fossil orangutan postcanine teeth from mainland Asia and Indonesia. We find few differences between regions, except for significantly lower average enamel thickness (AET) values in Indonesian mandibular first molars. Differences between fossil and extant orangutans are more marked, with fossil Pongo showing higher AET in most postcanine teeth. These differences are significant for maxillary and mandibular first molars. Fossil orangutans show higher AET than extant Pongo due to greater enamel cap areas, which exceed increases in enamel-dentine junction length (due to geometric scaling of areas and lengths for the AET index calculation). We also find greater dentine areas in fossil orangutans, but relative enamel thickness indices do not differ between fossil and extant taxa. When changes in dental tissue proportions between fossil and extant orangutans are compared with fossil and recent Homo sapiens, Pongo appears to show isometric reduction in enamel and dentine, while crown reduction in H. sapiens appears to be due to preferential loss of dentine. Disparate selective pressures or developmental constraints may underlie these patterns. Finally, the finding of moderately thick molar enamel in fossil orangutans may represent an additional convergent dental similarity with Homo erectus, complicating attempts to distinguish these taxa in mixed Asian faunas.
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    Extraction and sequencing of human and Neanderthal mature enamel proteins using MALDI-TOF/TOF MS
    (Elsevier BV, 2009) Nielsen-Marsh, Christina M.; Stegemann, Christin; Hoffmann, Ralf; Smith, Tanya; Feeney, Robin; Toussaint, Michel; Harvati, Katerina; Panagopoulou, Eleni; Hublin, Jean-Jacques; Richards, Michael P.
    We report here the first results of a method to extract and sequence mature enamel proteins from modern human and Neanderthal tooth enamel. Using MALDI-TOF/TOF mass spectrometry and a combination of direct sequencing and peptide mass mapping we have sequenced a peptide from the tyrosine-rich amelogenin peptide (TRAP) of the X isoform of the amelogenin protein for modern and recent human samples. We also report our results from two Neanderthal enamel samples where we were also able to recover fragments of the TRAP protein, which had a similar sequence to the modern human samples.
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    Brief communication: Dental development and enamel thickness in the Lakonis Neanderthal molar
    (Wiley-Blackwell, 2009) Smith, Tanya; Harvati, K.; Olejniczak, A.J.; Reid, D.J.; Hublin, J.-J.; Panagopoulou, E.
    Developmental and structural affinities between modern human and Neanderthal dental remains continue to be a subject of debate as well as their utility for informing assessments of life history and taxonomy. Excavation of the Middle Paleolithic cave site Lakonis in southern Greece has yielded a lower third molar (LKH 1). Here, we detail the crown development and enamel thickness of the distal cusps of the LKH 1 specimen, which has been classified as a Neanderthal based on the presence of an anterior fovea and mid-trigonid crest. Crown formation was determined using standard histological techniques, and enamel thickness was measured from a virtual plane of section. Developmental differences include thinner cuspal enamel and a lower periodicity than modern humans. Crown formation in the LKH 1 hypoconid is estimated to be 2.6–2.7 years, which is shorter than modern human times. The LKH 1 hypoconid also shows a more rapid overall crown extension rate than modern humans. Relative enamel thickness was approximately half that of a modern human sample mean; enamel on the distal cusps of modern human third molars is extremely thick in absolute and relative terms. These findings are consistent with recent studies that demonstrate differences in crown development, tissue proportions, and enamel thickness between Neanderthals and modern humans. Although overlap in some developmental variables may be found, the results of this and other studies suggest that Neanderthal molars formed in shorter periods of time than modern humans, due in part to thinner enamel and faster crown extension rates.